Here's what happens

* `f` is registered as a function in the global namespace

```{figure} /_static/lecture_specific/oop_intro/mutable1.png

:figclass: auto

```

* `x` bound to `[1]` in the global namespace

```{figure} /_static/lecture_specific/oop_intro/mutable2.png

:figclass: auto

```

* The call `f(x)`

* Creates a local namespace

* Adds `x` to the local namespace, bound to `[1]`

```{figure} /_static/lecture_specific/oop_intro/mutable3.png

:figclass: auto

```

```{note}

The global `x` and the local `x` refer to the same `[1]`

```

We can see the identity of local `x` and the identity of global `x` are the same

```{code-cell} python3

def f(x):

x[0] = x[0] + 1

print(f'the identity of local x is {id(x)}')

return x

x = [1]

print(f'the identity of global x is {id(x)}')

print(f(x), x)

```

* Within `f(x)`

* The list `[1]` is modified to `[2]`

* Returns the list `[2]`

* The local namespace is deallocated, and local `x` is lost

* Global `x` has been modified

```{figure} /_static/lecture_specific/oop_intro/mutable4.png

:figclass: auto

```

* The local namespace is deallocated, and the local `x` is lost

```{figure} /_static/lecture_specific/oop_intro/mutable5.png

:figclass: auto

```

If you want to modify the local `x` and the global `x` separately, you can create a [*copy*](https://docs.python.org/3/library/copy.html) of the list and assign the copy to the local `x`.

We will leave this for you to explore.

## Summary